Which muscle groups are primarily involved in shoulder extension?

Shoulder extension primarily involves the latissimus dorsi and teres major muscles. These muscles are key contributors to the movement where the arm is moved backward in relation to the body, which is the definition of shoulder extension. The latissimus dorsi, a large muscle of the back, plays a significant role in this action by contracting to pull the humerus posteriorly. Similarly, the teres major assists in this movement, also contributing to the adduction and medial rotation of the arm.

The other muscle groups mentioned do not play a primary role in shoulder extension. While the deltoids and pectorals can be involved in shoulder movements, their primary functions are more associated with shoulder flexion and abduction. The rotator cuff muscles are mainly responsible for stabilizing the shoulder joint during movement rather than facilitating shoulder extension specifically. The trapezius and rhomboids are primarily involved in movements related to scapular elevation and retraction, not directly in extending the shoulder.